The national capital's air quality turned severe on Monday evening as the pollution level increased again due to unfavourable meteorological conditions such as low wind speed, authorities said.
The overall air quality index (AQI) in the city was recorded at 407 which falls in the severe category, according to data provided by the Central Pollution Control Board (CPCB).
The PM2.5 (particles in the air with a diameter of less than 2.5 micrometres) level on Monday was recorded at 262 while the PM10 (particles in the air with a diameter of less than 10 micrometres) was recorded at 460, the CPCB said.
Nineteen areas in Delhi recorded severe air quality while 17 areas showed very poor air quality, it said, adding Ghaziabad, Faridabad, Greater Noida and Noida recorded severe air quality while Gurgaon showed improvement with the AQI being in the moderate category.
An AQI between 0 and 50 is considered "good", 51 and 100 "satisfactory", 101 and 200 "moderate", 201 and 300 "poor", 301 and 400 "very poor", and 401 and 500 "severe".
Satellite images by Centre-run System of Air Quality and Weather Forecasting (SAFAR) showed moderate stubble burning fire count that is contributing to seven per cent pollution at PM2.5 in Delhi.
Authorities have attributed the dip in air quality to unfavourable weather conditions such as low wind speed.
SAFAR said the air quality is likely to improve further by Tuesday but will remain in the "very poor" category.
"The stubble related impact continue to remain nominal due to slow transport height winds," it said.
The air quality in the national capital deteriorated severely on Thursday, a day after Diwali and continued to remain in the 'severe' category before showing a slight improvement on Saturday. Since then it has been oscillating between very poor and severe.
SAFAR said the air quality is likely to improve further by Tuesday but will remain in the 'very poor' category.